FTRACE's function tracer currently doesn't always work on ARM with
MODULE_PLT option enabled. If the module is loaded too far, FTRACE's
code modifier cannot cope with introduced veneers and turns the
function tracer off globally.
ARM64 already has a solution for the problem, refer to the following
patches:
arm64: ftrace: emit ftrace-mod.o contents through code
arm64: module-plts: factor out PLT generation code for ftrace
arm64: ftrace: fix !CONFIG_ARM64_MODULE_PLTS kernels
arm64: ftrace: fix building without CONFIG_MODULES
arm64: ftrace: add support for far branches to dynamic ftrace
arm64: ftrace: don't validate branch via PLT in ftrace_make_nop()
But the presented ARM variant has just a half of the footprint in terms of
the changed LoCs. It also retains the code validation-before-modification
instead of switching it off.
Changelog:
v2:
* As suggested by Steven Rostedt, refrain from tree-wide API modification,
save module pointer in dyn ftrace entry struct instead (PowerPC way)
Alexander Sverdlin (2):
ARM: PLT: Move struct plt_entries definition to header
ARM: ftrace: Add MODULE_PLTS support
arch/arm/include/asm/ftrace.h | 1 +
arch/arm/include/asm/module.h | 10 ++++++++
arch/arm/kernel/ftrace.c | 60 ++++++++++++++++++++++++++++++++++++-------
arch/arm/kernel/module-plts.c | 58 ++++++++++++++++++++++++++---------------
4 files changed, 100 insertions(+), 29 deletions(-)
--
2.4.6
No functional change, later it will be re-used in several files.
Signed-off-by: Alexander Sverdlin <[email protected]>
---
arch/arm/include/asm/module.h | 9 +++++++++
arch/arm/kernel/module-plts.c | 9 ---------
2 files changed, 9 insertions(+), 9 deletions(-)
diff --git a/arch/arm/include/asm/module.h b/arch/arm/include/asm/module.h
index 89ad059..6996405 100644
--- a/arch/arm/include/asm/module.h
+++ b/arch/arm/include/asm/module.h
@@ -19,6 +19,15 @@ enum {
};
#endif
+#define PLT_ENT_STRIDE L1_CACHE_BYTES
+#define PLT_ENT_COUNT (PLT_ENT_STRIDE / sizeof(u32))
+#define PLT_ENT_SIZE (sizeof(struct plt_entries) / PLT_ENT_COUNT)
+
+struct plt_entries {
+ u32 ldr[PLT_ENT_COUNT];
+ u32 lit[PLT_ENT_COUNT];
+};
+
struct mod_plt_sec {
struct elf32_shdr *plt;
int plt_count;
diff --git a/arch/arm/kernel/module-plts.c b/arch/arm/kernel/module-plts.c
index 3d0c2e4..f272711 100644
--- a/arch/arm/kernel/module-plts.c
+++ b/arch/arm/kernel/module-plts.c
@@ -14,10 +14,6 @@
#include <asm/cache.h>
#include <asm/opcodes.h>
-#define PLT_ENT_STRIDE L1_CACHE_BYTES
-#define PLT_ENT_COUNT (PLT_ENT_STRIDE / sizeof(u32))
-#define PLT_ENT_SIZE (sizeof(struct plt_entries) / PLT_ENT_COUNT)
-
#ifdef CONFIG_THUMB2_KERNEL
#define PLT_ENT_LDR __opcode_to_mem_thumb32(0xf8dff000 | \
(PLT_ENT_STRIDE - 4))
@@ -26,11 +22,6 @@
(PLT_ENT_STRIDE - 8))
#endif
-struct plt_entries {
- u32 ldr[PLT_ENT_COUNT];
- u32 lit[PLT_ENT_COUNT];
-};
-
static bool in_init(const struct module *mod, unsigned long loc)
{
return loc - (u32)mod->init_layout.base < mod->init_layout.size;
--
2.4.6
Teach ftrace_make_call() and ftrace_make_nop() about PLTs.
Teach PLT code about FTRACE and all its callbacks.
Otherwise the following might happen:
------------[ cut here ]------------
WARNING: CPU: 14 PID: 2265 at .../arch/arm/kernel/insn.c:14 __arm_gen_branch+0x83/0x8c()
...
Hardware name: LSI Axxia AXM55XX
[<c0314a49>] (unwind_backtrace) from [<c03115e9>] (show_stack+0x11/0x14)
[<c03115e9>] (show_stack) from [<c0519f51>] (dump_stack+0x81/0xa8)
[<c0519f51>] (dump_stack) from [<c032185d>] (warn_slowpath_common+0x69/0x90)
[<c032185d>] (warn_slowpath_common) from [<c03218f3>] (warn_slowpath_null+0x17/0x1c)
[<c03218f3>] (warn_slowpath_null) from [<c03143cf>] (__arm_gen_branch+0x83/0x8c)
[<c03143cf>] (__arm_gen_branch) from [<c0314337>] (ftrace_make_nop+0xf/0x24)
[<c0314337>] (ftrace_make_nop) from [<c038ebcb>] (ftrace_process_locs+0x27b/0x3e8)
[<c038ebcb>] (ftrace_process_locs) from [<c0378d79>] (load_module+0x11e9/0x1a44)
[<c0378d79>] (load_module) from [<c037974d>] (SyS_finit_module+0x59/0x84)
[<c037974d>] (SyS_finit_module) from [<c030e981>] (ret_fast_syscall+0x1/0x18)
---[ end trace e1b64ced7a89adcc ]---
------------[ cut here ]------------
WARNING: CPU: 14 PID: 2265 at .../kernel/trace/ftrace.c:1979 ftrace_bug+0x1b1/0x234()
...
Hardware name: LSI Axxia AXM55XX
[<c0314a49>] (unwind_backtrace) from [<c03115e9>] (show_stack+0x11/0x14)
[<c03115e9>] (show_stack) from [<c0519f51>] (dump_stack+0x81/0xa8)
[<c0519f51>] (dump_stack) from [<c032185d>] (warn_slowpath_common+0x69/0x90)
[<c032185d>] (warn_slowpath_common) from [<c03218f3>] (warn_slowpath_null+0x17/0x1c)
[<c03218f3>] (warn_slowpath_null) from [<c038e87d>] (ftrace_bug+0x1b1/0x234)
[<c038e87d>] (ftrace_bug) from [<c038ebd5>] (ftrace_process_locs+0x285/0x3e8)
[<c038ebd5>] (ftrace_process_locs) from [<c0378d79>] (load_module+0x11e9/0x1a44)
[<c0378d79>] (load_module) from [<c037974d>] (SyS_finit_module+0x59/0x84)
[<c037974d>] (SyS_finit_module) from [<c030e981>] (ret_fast_syscall+0x1/0x18)
---[ end trace e1b64ced7a89adcd ]---
ftrace failed to modify [<e9ef7006>] 0xe9ef7006
actual: 02:f0:3b:fa
ftrace record flags: 0
(0) expected tramp: c0314265
Signed-off-by: Alexander Sverdlin <[email protected]>
---
arch/arm/include/asm/ftrace.h | 1 +
arch/arm/include/asm/module.h | 1 +
arch/arm/kernel/ftrace.c | 60 ++++++++++++++++++++++++++++++++++++-------
arch/arm/kernel/module-plts.c | 53 ++++++++++++++++++++++++++++----------
4 files changed, 93 insertions(+), 22 deletions(-)
diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
index 9e842ff..3e663f9 100644
--- a/arch/arm/include/asm/ftrace.h
+++ b/arch/arm/include/asm/ftrace.h
@@ -19,6 +19,7 @@ struct dyn_arch_ftrace {
#ifdef CONFIG_OLD_MCOUNT
bool old_mcount;
#endif
+ struct module *mod;
};
static inline unsigned long ftrace_call_adjust(unsigned long addr)
diff --git a/arch/arm/include/asm/module.h b/arch/arm/include/asm/module.h
index 6996405..e3d7a51 100644
--- a/arch/arm/include/asm/module.h
+++ b/arch/arm/include/asm/module.h
@@ -30,6 +30,7 @@ struct plt_entries {
struct mod_plt_sec {
struct elf32_shdr *plt;
+ struct plt_entries *plt_ent;
int plt_count;
};
diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
index 5617932..eff306c 100644
--- a/arch/arm/kernel/ftrace.c
+++ b/arch/arm/kernel/ftrace.c
@@ -98,6 +98,19 @@ int ftrace_arch_code_modify_post_process(void)
static unsigned long ftrace_call_replace(unsigned long pc, unsigned long addr)
{
+ s32 offset = addr - pc;
+ s32 blim = 0xfe000008;
+ s32 flim = 0x02000004;
+
+ if (IS_ENABLED(CONFIG_THUMB2_KERNEL)) {
+ blim = 0xff000004;
+ flim = 0x01000002;
+ }
+
+ if (IS_ENABLED(CONFIG_ARM_MODULE_PLTS) &&
+ (offset < blim || offset > flim))
+ return 0;
+
return arm_gen_branch_link(pc, addr);
}
@@ -166,10 +179,22 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
unsigned long new, old;
unsigned long ip = rec->ip;
+ unsigned long aaddr = adjust_address(rec, addr);
old = ftrace_nop_replace(rec);
- new = ftrace_call_replace(ip, adjust_address(rec, addr));
+ new = ftrace_call_replace(ip, aaddr);
+
+#ifdef CONFIG_ARM_MODULE_PLTS
+ if (!new) {
+ struct module *mod = rec->arch.mod;
+
+ if (mod) {
+ aaddr = get_module_plt(mod, ip, aaddr);
+ new = ftrace_call_replace(ip, aaddr);
+ }
+ }
+#endif
return ftrace_modify_code(rec->ip, old, new, true);
}
@@ -199,20 +224,37 @@ int ftrace_make_nop(struct module *mod,
unsigned long new;
int ret;
- old = ftrace_call_replace(ip, adjust_address(rec, addr));
- new = ftrace_nop_replace(rec);
- ret = ftrace_modify_code(ip, old, new, true);
+ /* mod is only supplied during module loading */
+ if (!mod)
+ mod = rec->arch.mod;
+ else
+ rec->arch.mod = mod;
-#ifdef CONFIG_OLD_MCOUNT
- if (ret == -EINVAL && addr == MCOUNT_ADDR) {
- rec->arch.old_mcount = true;
+ for (;;) {
+ unsigned long aaddr = adjust_address(rec, addr);
+
+ old = ftrace_call_replace(ip, aaddr);
+
+#ifdef CONFIG_ARM_MODULE_PLTS
+ if (!old && mod) {
+ aaddr = get_module_plt(mod, ip, aaddr);
+ old = ftrace_call_replace(ip, aaddr);
+ }
+#endif
- old = ftrace_call_replace(ip, adjust_address(rec, addr));
new = ftrace_nop_replace(rec);
ret = ftrace_modify_code(ip, old, new, true);
- }
+
+#ifdef CONFIG_OLD_MCOUNT
+ if (ret == -EINVAL && !rec->arch.old_mcount) {
+ rec->arch.old_mcount = true;
+ continue;
+ }
#endif
+ break;
+ }
+
return ret;
}
diff --git a/arch/arm/kernel/module-plts.c b/arch/arm/kernel/module-plts.c
index f272711..a216256 100644
--- a/arch/arm/kernel/module-plts.c
+++ b/arch/arm/kernel/module-plts.c
@@ -7,6 +7,7 @@
*/
#include <linux/elf.h>
+#include <linux/ftrace.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/sort.h>
@@ -22,6 +23,15 @@
(PLT_ENT_STRIDE - 8))
#endif
+static u32 fixed_plts[] = {
+ FTRACE_ADDR,
+ MCOUNT_ADDR,
+#ifdef CONFIG_OLD_MCOUNT
+ (unsigned long)ftrace_caller_old,
+ (unsigned long)mcount,
+#endif
+};
+
static bool in_init(const struct module *mod, unsigned long loc)
{
return loc - (u32)mod->init_layout.base < mod->init_layout.size;
@@ -31,26 +41,43 @@ u32 get_module_plt(struct module *mod, unsigned long loc, Elf32_Addr val)
{
struct mod_plt_sec *pltsec = !in_init(mod, loc) ? &mod->arch.core :
&mod->arch.init;
+ int idx;
+ struct plt_entries *plt;
+
+ /* Pre-allocate entries in the first plt */
+ if (!pltsec->plt_count) {
+ plt = (struct plt_entries *)pltsec->plt->sh_addr;
+ for (idx = 0; idx < ARRAY_SIZE(plt->ldr); ++idx)
+ plt->ldr[idx] = PLT_ENT_LDR;
+ memcpy(plt->lit, fixed_plts, sizeof(fixed_plts));
+ pltsec->plt_count = ARRAY_SIZE(fixed_plts);
+ /*
+ * cache the address,
+ * ELF header is available only during module load
+ */
+ pltsec->plt_ent = plt;
+ }
+ plt = pltsec->plt_ent;
- struct plt_entries *plt = (struct plt_entries *)pltsec->plt->sh_addr;
- int idx = 0;
+ idx = ARRAY_SIZE(fixed_plts);
+ while (idx)
+ if (plt->lit[--idx] == val)
+ return (u32)&plt->ldr[idx];
/*
* Look for an existing entry pointing to 'val'. Given that the
* relocations are sorted, this will be the last entry we allocated.
* (if one exists).
*/
- if (pltsec->plt_count > 0) {
- plt += (pltsec->plt_count - 1) / PLT_ENT_COUNT;
- idx = (pltsec->plt_count - 1) % PLT_ENT_COUNT;
+ plt += (pltsec->plt_count - 1) / PLT_ENT_COUNT;
+ idx = (pltsec->plt_count - 1) % PLT_ENT_COUNT;
- if (plt->lit[idx] == val)
- return (u32)&plt->ldr[idx];
+ if (plt->lit[idx] == val)
+ return (u32)&plt->ldr[idx];
- idx = (idx + 1) % PLT_ENT_COUNT;
- if (!idx)
- plt++;
- }
+ idx = (idx + 1) % PLT_ENT_COUNT;
+ if (!idx)
+ plt++;
pltsec->plt_count++;
BUG_ON(pltsec->plt_count * PLT_ENT_SIZE > pltsec->plt->sh_size);
@@ -182,8 +209,8 @@ static unsigned int count_plts(const Elf32_Sym *syms, Elf32_Addr base,
int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
char *secstrings, struct module *mod)
{
- unsigned long core_plts = 0;
- unsigned long init_plts = 0;
+ unsigned long core_plts = ARRAY_SIZE(fixed_plts);
+ unsigned long init_plts = ARRAY_SIZE(fixed_plts);
Elf32_Shdr *s, *sechdrs_end = sechdrs + ehdr->e_shnum;
Elf32_Sym *syms = NULL;
--
2.4.6
On Thu, 1 Mar 2018 17:43:43 +0100
Alexander Sverdlin <[email protected]> wrote:
> diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
> index 9e842ff..3e663f9 100644
> --- a/arch/arm/include/asm/ftrace.h
> +++ b/arch/arm/include/asm/ftrace.h
> @@ -19,6 +19,7 @@ struct dyn_arch_ftrace {
> #ifdef CONFIG_OLD_MCOUNT
> bool old_mcount;
> #endif
I think you want to add:
#ifdef CONFIG_ARM_MODULE_PLTS
> + struct module *mod;
#endif
This will add more memory overhead, and we don't want to add that if it
is not needed.
-- Steve
Hello Steven!
On 02/03/18 18:00, Steven Rostedt wrote:
>> diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
>> index 9e842ff..3e663f9 100644
>> --- a/arch/arm/include/asm/ftrace.h
>> +++ b/arch/arm/include/asm/ftrace.h
>> @@ -19,6 +19,7 @@ struct dyn_arch_ftrace {
>> #ifdef CONFIG_OLD_MCOUNT
>> bool old_mcount;
>> #endif
> I think you want to add:
>
> #ifdef CONFIG_ARM_MODULE_PLTS
>> + struct module *mod;
> #endif
>
> This will add more memory overhead, and we don't want to add that if it
> is not needed.
Will include it into the next version.
Thanks for the review!
--
Best regards,
Alexander Sverdlin.